The use of polyethylene compositions, such as linear low density polyethylenes and/or high density polyethylenes, in fabrication of injection molded articles is generally known. Any conventional method, such as gas phase process, slurry process, solution process or high pressure process, may be employed to produce such polyethylene compositions.
In general, in the injection molding process, a polyethylene composition is fed into an extruder via a hopper. The extruder conveys, heats, melts, and pressurizes the polyethylene composition to a form a molten stream. The molten stream is forced out of the extruder under pressure through a nozzle into a relatively cool mold held closed thereby filling the mold under pressure. The melt cools and hardens until fully set-up. The mold then is opened and the molded article, e.g. tote, dish pan, waist container, bottle cap, is removed.
Various polymerization techniques using different catalyst systems have been employed to produce such polyethylene compositions suitable for injection molding applications. However, the currently available polyethylene compositions fail to provide a stiffness/toughness balance that is required for injection moldings applications, e.g. thin wall articles with improved cold temperature performance.
Despite the research efforts in developing polyethylene compositions suitable for injection molding, there is still a need for a polyethylene composition having a narrow molecular weight distribution, narrow composition distribution, and improved low and room temperature impact resistance while maintaining stiffness and processability properties. Additionally, there is a need for a method of producing such polyethylene compositions having a narrow molecular weight distribution, narrow composition distribution, and improved low temperature impact resistance while maintaining stiffness and processability properties.